Base 21 Repunits
Table
Format: small prime × proven prime<size> × (probable prime)<size> × [composite]<size> × {unknown}<size>
| 69: | \[{21^{69}-1\over20}\] | 47 × 463 × 19597 × 459878292118921111<18> × 139870566115103282847737<24> × 31179105887601949149105715319437017328831<41> |